A crop is attacked by several diseases. For example, potato is attacked by early and late blight, black scurf, root knot and several viral diseases. Each disease has specific control measures. It is not necessary that the control measure for one disease will control other diseases also. Therefore for controlling a number of major diseases the causal agents their mode of spread and activity should be taken into account. The approach should be so coordinated that the maximum number of diseases can be controlled partly or fully by minimum number of operations, this multiple disease control method can reduce the cost of plant protection giving the grower considerable ease in applying them. For instance all potato diseases can be checked by adopting the following measures.
Is disease control by individual farmer effective?
For any effective control measure its adoption on a large contiguous area is necessary as pathogens are disseminated through air, water, insects or by shifting of soil. It is quite impossible to raise an effective and permanent barrier against these agencies transmitting plant diseases.
Suppose one farmer in the affected area follows certain control measures in this field to remove a particular disease, but his neighboring farmers are not practicing them in their crop. In such a situation there will not be much effect of control, because later on pathogens will transmit again to the controlled field from its neighboring affected fields. To avoid such a situation, the individual farmer may have to spend more money, time and energy in repeating the control measures. Therefore, if control measures such as chemical spraying on standing crop or crop rotation or deep ploughing are adopted on cooperative basis over adjoining areas under a crop its effectiveness or chances of success would be much more.
How to decide proper control in relation to disease cycle ?
For effective and economic control in relation to disease cycle is necessary:
For destroying the pathogen or suppressing its growth, knowledge of the various aspects of disease cycle is helpful. The correct knowledge about the cause of disease can prevent new problems and reduce expenses. For example yellowing of rice or wheat leaves or stunted growth of their plant may not necessary be due to pathogen. It may be due to nutritional deficiency or improper drainage. Here we have to apply nutrients or provide proper drainage instead of applying any chemical.
Similarly, a disease may be sea-borne or spread through wind. Based on this information, the farmer can decide on seed treatment by a systemic chemical, which can kill the pathogen or some other measure like removal of diseases from the field. Similarly, loose smut of wheat can also be controlled by the same measures. The knowledge of environmental relations makes it possible to determine the time of appearance and severity of the disease so that preventive measures can be adopted more accurately.
Always consider cost-benefit ratio
The plant disease reduces economic gain from the crop. The aim of disease control is to check this reduction. A farmer can adopt any control measure if it is beneficial in terms of money. Acceptance of any control measure will thus depend upon cost-benefit ratio. If a farmer sees more benefit in spraying chemical instead of control measures, then it is difficult to convince him about adopting cultural practices for controlling diseases.